Process for dehydrating benzene



June 20, 1961 o. H. HARIU ETAL 2,989,572

PROCESS FOR DEHYDRATING BENZENE Filed March 20, 1958 2 Sheets-Sheet l Dried Hydrocarbon Liquid Hydrocarbon Layer 4/ 1 i H Caustic 2 w E Solution C A l 3 E r I Caustic Layer 0.

6 l2 5 P I We? Hydrocarbon 7 w? 1 Liquid Di lured Caustic 10 Process INVENTORS O. H. HARIU J- E WOODBRIDGE WM 5 AM ATTORNEY June 20, 1961 Filed March 20, 1958 Fig. 2

PPM (By WT.) Water in Benzene o. H. HARIU ETAL 2,989,572

PROCESS FOR DEHYDRATING BENZENE 2 Sheets-Sheet 2 Solubility of water in Benzol m Contact with NaOH Solutions (Having the Goncentratians Noted Above Each Curve) I I I I20 I I I 8 0 [00 HO I30 Temperature INVENTORS O.H, HARIU d. E. WOODBRIDGE ATTORNEY United States Patent fiice syl Filed Mar. 20, 1958, Ser. No. 722,663 2 Claims. (Cl. 260-674) This invention relates to a method of dehydrating hydrocarbons. More particularly this invention relates to an improved method of dehydrating hydrocarbons which are substantially chemically inert to caustic alkalies. In one specific embodiment this invention relates to an improved methodfor drying benzene.

Caustic alkali solutions have longbeen' usedas dehydrating agents for hydrocarbons. Difi'c'ulties are encountered, however, in securing substantially}completedehydration as well as in precluding. the formation of emulsions or the entrainment of caustic in the hydrocarbons or of hydrocarbons in the caustic.

The instant invention has as an 'objeetthe accomplishment of substantially complete dehydration of hydrocarbons or dehydration to a desired water content, It has also as an object the avoidance of the formation of emulsions in the dehydration process. Another object is to obviate the entrainment of caustic and hydrocarbons in each other. Other objects and advantages will be apparent from a reading of the specification and the apj pended claims.

Broadly stated, these objects are accomplished in the instant invention by dispersing the hydrocarbons as jets at a specific velocity through a layer of caustic alkali solution of a specific depth, the hydrocarbon layer formed having a specific superficial velocity, as described hereinafter.

It has been discovered that substantial improvements in the drying of hydrocarbons by the use of caustic alkali solutions can be attained by dispersing the hydrocarbon through the alkali solution by means of a perforated distributor ring, or other suitable distributing means, so that the hydrocarbon issues from the holes as jets with a velocity of 2 to feet per second. Holes ranging in diameter from Vs" to have been found most suitable. The jets break up into individual drops as the hydrocarbon rises through the caustic layer which is maintained at a level of at least two feet, and preferably between 2 to 8 feet, by a level controller consisting of a float or differential pressure measuring device or other suitable device. The diameter of the drying vessel is chosen so that the upward velocity in the hydrocarbon layer is not greater than 500 gallons per hour per square foot of cross sec tional area of the vessel and preferably between 200 to 500 gallons per hour per square foot. In order to remove entrained caustic droplets the hydrocarbon passes through a coalescer consisting of steel wool or other suitable material before it leaves the drying vessel.

The velocity of the hydrocarbon jets must be maintained between 2 to 10 feet per second. It was found that a velocity below two feet per second results in inefiicient contact with the caustic alkali layer while at a velocity above ten feet per second emulsion problems or entrainment of caustic in the efiluent hydrocarbon or hydrocarbon in the efiiuent caustic may result.

The depth of the caustic alkali layer should be at least two feet, otherwise insufiicient contact will be provided for the hydrocarbons. It is preferred to maintain a level of caustic solution ranging from 2 to 8 feet in depth. The caustic solution may be added continuously and withdrawn under level control as described hereinbefore, thus providing a constant hydrocarbon eliiuent water content, or successive batches of caustic solution may be added.

Pa ten ted .lune 20, 19.61

The amount of drying can be controlled by regulating the strength at which the caustic is removed. In the continuous process the strength of the caustic withdrawn depends on the caustic feed strength, the withdrawal rate, and the amount of water removed.

The drying vessel diameter should be such that the hydrocarbon superficial velocity is not greater than 500 gallons per hour per square foot. Above this velocity caustic entrainment may result. Velocities ranging between 200 and 500 gallons per hour per square foot are preferred. a h

As a specific embodiment the utilityof the instant invention will be demonstrated by the dehydration of benzene which will be described in connection with the accompanying drawings. The '.process, of course, "is adapted for use with other hydrocarbons. I

'Referring to FIGURE 1, a 50 weight percent sodium hydroxide solution is-charged to line 1 and pumped at the rate of 31 gallons per hour by pump 2 through line'3 into vessel 4 in which the solution is maintained at a level of 2 to 8 feet in layer 9. The caustic level is maintained by a level controller 11 which actuate valve 14' through air line 12 and diaphragm 13. A benzene stream of 1800 gallons per hour containing 1400 p.p.m. by weight of water at F., is charged to line 5 and pumped by pump 6 through line 7 to distributor ring 8 which contains a series of 4" holes 17. The benzene issues from the holes as jets with a velocity of 2 to 10 feet per second. The jets break up into individual drops as the hydrocarbon rises through the caustic layer. At the interface between layers 9 and 10 the drops coalesce and form into a single hydrocarbon layer 10. The upward velocity in the hydrocarbon layer 10 ranges between 200 to 500 gallons per hour per square foot. The benzene passes through a steel wool coalescer 18 to remove entrained caustic droplets and flows out through line 19 with a water content of p.p.m. Diluted caustic (48 weight percent NaOH) flows from the bottom of vessel 4 through line 15, valve 14 and line 16 to a downstream process.

The quantity and concentration of the inlet caustic solution in this specific example were determined by the caustic requirement of the downstream process and the dryness desired for the hydrocarbon stream. This particular process required 44 gallons per hour of 38 weight percent NaOH. It was desired to dehydrate the benzene to a water content of 150 p.p.m. so that it could be utilized in an alkylation process. A series of solubility curves of water in benzene in contact with varying concentrations of NaOH solutions was calculated from the solubility of water in benzene, the vapor pressure of water, and the vapor pressure of water over the NaOH solutions. These curves are shown in FIGURE 2. It was determined from FIGURE 2 that a 48 weight percent NaOH solution would be in equilibrium with 150 p.p.m. water in benzene at 125 F. Thus, the dilute caustic leaving the drying vessel would have a concentration of 48 weight percent and would subsequently be diluted to 38 weight percent. The water removed from the benzene amounted to 15 pounds per hour. From the requirement of 44 gallons per hour of 38 percent caustic, the fact that the caustic leaving the drying vessel should have a concentration of 48 percent and the 15 pound per hour w-ater pickup, it can be calculated that the caustic feed should be 31 gallons per hour of 50 Weight percent NaOH.

The efiiciency of the instant process is demonstrated by the fact that equilibrium is essentially attained; that is, the water in the dehydrated hydrocarbon is in equilibrium with the water in the efiiuent caustic solution.

The process of the instant invention may be adapted for use in the dehydration of any hydrocarbon which is substantially chemically inert to caustic alkalies, including both aliphatic and aromatic hydrocarbons. Although sodium hydroxide is preferred as a dehydration agent potassium hydroxide may be employed as well. It is preferred to utilize caustic alkali solutions ranging in concentration from 25 to 70 weight percent, the concentration depending in part on the amount of dehydration desired as well as on the requirements of any downstream process associated with the dehydration process.

Since many apparently different embodiments of this invention may be made without departing from the spirit thereof, it is to be understood that the instant invention is not to be limited to the specific embodiment thereof except as indicated in the appended claims.

We claim:

1. In the process for the dehydration of liquid benzene by treatment with sodium hydroxide solutions, the improvement which consists essentially of controlling the dehydration of the benzene so as to obtain a predetermined water content therein not in excess of from 230 parts per million to 1500 parts per million at temperatures ranging from 50 F. to 160 F. in accordance with FIGURE 2 of the drawings by dispersing the benzene as jets at a velocity of 2 to feet per second through a layer of sodium hydroxide solution ranging in concentration from about 25 weight percent to 70 weight percent and having a depth ranging from about 2 feet to about 8 feet, the superficial velocity of the benzene layer formed being no greater than 500 gallons per hour per square foot.

2. In the process for the dehydration of liquid benzene by treatment with sodium hydroxide solutions, the in1- provement which consists essentially of controlling the dehydration of the benzene so as to obtain a predetermined water content therein not in excess of from 230 parts per million to 1500 parts per million at temperatures ranging from F. to 160 F. in accordance with FIG- URE 2 of the drawings by dispersing the benzene as jets at a velocity of 2 to 10 feet per second through a layer of sodium hydroxide solution ranging in concentration from about 25 weight percent to weight percent and having a depth ranging from about 2 feet to about 8 feet,

the superficial velocity of the benzene layer formed ranging from about 200 gallons to about 500 gallons per hour per square foot.

References Cited in the file of this patent UNITED STATES PATENTS 

1. IN THE PROCESS FOR THE DEHYDRATION OF LIQUID BENZENE BY TREATMENT WITH SODIUM HYDROXIDE SOLUTIONS, THE IMPROVEMENT WHICH CONSISTS ESSENTIALLY OF CONTROLLING THE DEHYDRATION OF THE BENZENE SO AS TO OBTAIN A PREDETERMINED WATER CONTENT THEREIN NOT IN EXCESS OF FROM 230 PARTS PER MILLION TO 1500 PARTS PER MILLION AT TEMPERATURES RANGING FROM 50*F. TO 160*F. IN ACCORDANCE WITH FIGURE 2 OF THE DRAWINGS BY DISPERSING THE BENZENE AS JETS AT A VELOCITY OF 2 TO 10 FEET PER SECOND THROUGH A LAYER OF SODIUM HYDROXIDE SOLUTION RANGING IN CONCENTRA- 